This invention relates to high-strength spring steels which can be used as a material for high-strength springs in form of hot formed coil spring or cold formed coil spring for use in automobiles, airplane equipments, various industrial machines, various agricultural machines and the like as well as a method of producing the same.
2. Description of the Related Art
Heretofore, the manufacture of coil springs is roughly classified into hot forming and cold forming.
In case of the hot forming, the steel material is hot coiled, subjected to a heat treatment such as quench hardening and tempering, and thereafter subjected to shot peening and setting.
In case of the cold forming, the steel material is subjected to an oil tempering, cold coiled and thereafter subjected to shot peening and setting.
On the other hand, there are made various attempts for increasing the strength of the spring and more improving fatigue limit thereof. Among them, it is attempted to adjust the chemical composition of steel for more increasing the strength of the spring and improving the fatigue limit.
In the conventional springs made from the starting material for the production of high-strength spring steel, however, the increase of the strength and the improvement of the fatigue limit are critical only by the adjustment of the chemical composition, so that there is a problem that it is difficult to stably obtain high-strength springs. Therefore, it is demanded to solve the above problems.